1. Field of the Invention
This invention relates to apparatus and method for determining the rate of flow of a fluid by measuring the potential difference developed in the fluid as it moves through a magnetic field produced by an electromagnet.
2. Background Information
In a magnetic flow meter an electrical potential difference developed in the fluid is detected by a pair of electrodes spaced apart from each other along a line generally orthogonal to both the direction in which the flow is measured and a magnetic field. This arrangement is used both in full bore sensors, where the electrodes are typically mounted in electrically insulated liners inside of metal shells, and in insertion probe meters, where the electrodes are mounted on a bottom or side of a probe.
In typical operation the magnetic field is periodically energized to provide a stable magnetic field for a period of time during which the difference in the electrode signal is amplified and detected to provide a measure of flow rate. Although various methods, such as the reversal of the magnetic field polarity and referencing to electrode signal potential in the absence of the magnetic field, are employed in the current art to reduce drift and susceptibility to interfering signals, these problems can still be troublesome. These problems are commonly more severe when the sensor is configured as a probe, which has smaller spacing between sensing electrodes than does a full-bore meter, which leads to a reduction in the magnitude of the sensed voltage and thus to a reduced signal to noise ratio.